1. Field of the Invention
This invention relates to an image forming apparatus which is equipped with storage means for storing a recording medium, and feed means including first and second paper feed rollers, said first paper feed roller delivering the recording medium from the storage means and abutting it to said second paper feed roller and said second paper feed roller feeding the abutted recording medium to an image forming unit.
The present invention relates also to an image forming apparatus which includes scanning means for scanning a document placed on a document glass plate, scan-driving means for driving this scanning means, storage means for storing a recording medium, detection means for detecting the size of the recording medium stored in the storing means and feed means for feeding the recording medium, and which forms an image on the fed recording medium by use of image information obtained by the scanning means.
2. Description of the Prior Art
A prior art example will be explained with reference to the accompanying drawings. FIG. 6 is a structural view of an electrophotographic reproducing apparatus as a prior art example.
In FIG. 6, a document glass plate 1 which is made of transparent glass and on which a document D is to be placed is disposed at the center of the upper portion of a reproducing apparatus main body and a scale plate 2 for designating the placement position in accordance with the size of the document D is disposed at the left end of the document glass plate 1. A document cover 3 capable of covering the document D placed on the document glass plate 1 is disposed at the upper part of this plate 1 in such a manner as to be capable of turning down forwardly. The document D is placed on the document glass plate 1 in match with the scale designated by the scale plate 2 and when covered with the document cover 3, its movement is restricted.
A first mirror unit 6 equipped with an exposure lamp 4 and a first mirror 5 is disposed below the document glass plate 1 and inside the reproducing apparatus main body in such a manner as to be capable of moving linearly to the right and left in FIG. 6 in parallel with the document glass plate 1, and capable of scanning the full surface of the document D. A second mirror unit 9 formed by integrating second and third mirrors 7 and 8 can linearly move to the right and left in FIG. 4 and in parallel with the document glass plate 1 at the speed which is the half of the first mirror unit 6 in such a manner as to keep a predetermined optical path length. A main lens 10 is the lens to which the reflected rays of light from the document D on the document glass plate 1 are incident after being reflected by the first, second and third mirrors 5, 7, 8, and the rays of light leaving this main lens 10 are incident into a photosensitive drum 12 as an image retainer through a fourth mirror 11 and through a slit 13. These first and second mirror units 6 and 9 are driven by an optical system driving motor not shown in the drawing.
A charging electrode 14 charges uniformly the photosensitive drum 12. Accordingly, electrostatic latent images are formed sequentially on the photosensitive drum 12 rotating clockwise in FIG. 6 due to the incidence of rays of light from the optical system described above. A developing device 15 converts the electrostatic latent image on this photosensitive drum 12 to a visible toner image.
On the other hand, a paper feeder for feeding transfer paper comprises a paper cassette 16 for storing transfer paper (recording medium) P, a first paper feed roller 17 for delivering one by one this transfer paper P from the paper cassette 16, a second paper feed roller 18 for feeding delivered transfer paper P to the photosensitive drum 12 side, and guide plates 19 and 20 disposed between the paper cassette 16 and the second paper feed roller 18 and between the second paper feed roller 18 and a transfer electrode which will be described later. At the time of reproduction, transfer paper P inside the paper cassette 16 is delivered by the first paper feed roller 17 and is abutted against the second paper feed roller 18 while being guided by the guide plate 19. The second paper feed roller 18 is driven by a paper feed timing signal which brings the tip of the toner image on the photosensitive drum 12 into conformity with the tip of transfer paper P.
A transfer electrode 21 transfers the toner image on the photosensitive drum 12 onto transfer paper P and a separating electrode 22 separates transfer paper P from the photosensitive drum 12. Transfer paper P separated there is sent to a fixing device 24 through transfer paper conveyor means 23, is subjected to fusion-fixing by a heat-fixing roller and a press roller and is thereafter discharged by a paper discharge roller 25 onto a paper tray 26. These first paper feed roller 17, second paper feed roller 18, photosensitive drum 12 and paper discharge roller 25 are driven by a paper feed system driving motor which is not shown in the drawing.
After the transfer step is complete, the toner remaining on the photosensitive drum 12 is removed by a cleaning device 27. In order to make this removal easy, a cleaning/charge eliminating electrode 28 for effecting A.C. corona discharge is disposed at its pre-stage. A charge eliminating unit 29 for erasing the charge of the non-image portions is disposed at the post-stage of the charging electrode 14 so as to prevent the toner from attaching to the non-image portions and in such a manner as to face the photosensitive drum 12. Incidentally, reference numerals 30 and 31 represent a precharge exposure unit and an exposure unit before transfer, respectively.
In the prior art example having the construction described above, the second paper feed roller 18 is driven by the paper feed timing signal such that the tip of the toner image on the photosensitive drum 12 is in conformity with the tip of transfer paper P. This timing signal is generated from a timing sensor, not shown, when the first mirror unit 6 reaches a predetermined position.
If the size of transfer paper P is different at the time of the feed of paper by the second paper feed roller, however, the load of frictional resistance by the first paper feed roller 17 and the guide plate 19 becomes different. Accordingly, there is a problem that the tip of the toner image on the photosensitive drum 12 is not in conformity with the tip of transfer paper P depending on the size of recording paper P.
If the paper cassette 16 has a two-stage structure, the timing signal is generated at the same timing for both transfer paper P which is supplied from the paper cassette 16 of the upper stage and transfer paper P which is supplied from the paper cassette 16 of the lower stage.
However, the paper feed path (the route from each paper cassette 16 to the second paper feed roller 18) is different between transfer paper P supplied from the paper cassette 16 of the upper stage and transfer paper P supplied from the paper cassette 16 of the lower stage. Since transfer paper P is fed while it keeps sliding contact with the paper feed path, a delicate sliding difference occurs on the second paper feed roller 18 depending on the level of the frictional resistance to transfer paper P and therefore the problems occurs in that the tip of the toner image on the photosensitive drum 12 does not coincide with the tip of transfer paper P.
In the prior art example having the construction described above, transfer paper P is supplied while keeping sliding contact with the paper feed path. Accordingly, if the size of transfer paper P is different at the time of the paper feed by the second paper feed roller 18, the load of the frictional resistance due to the first paper feed roller 17 and the guide plate 19 varies. This difference of the size of transfer paper P causes a delicate sliding difference of the second paper feed roller 18 and results in the difference of the paper feed speed.
On the other hand, the optical system (scanning system) and the paper feed system are driven by separate motors, respectively. Therefore, there is a problem that the length of an image of the document D in the paper feed direction obtained by scanning is different from the length of an image in the paper feed direction transferred onto transfer paper P depending on the size of transfer paper P.
In the prior art example having the construction described above, the paper feed path (the route from each paper cassette 16 to the second paper feed roller 18) is different between transfer paper P supplied from the paper cassette 16 of the upper stage and transfer paper P supplied from the paper cassette 16 of the lower stage. Since transfer paper P is supplied while keeping sliding contact with the paper feed path, a delicate sliding difference occurs at the second paper feed roller 18 depending on the level of the frictional resistance to transfer paper P and a difference of the paper feed speed occurs depending on the position of the paper feed cassette 16.
However, since the optical system (scanning system) and the paper feed system are driven by separate motors, respectively, there occurs a problem that the length of the image of the document D in the paper feed direction obtained by scanning is different from the length of the image transferred actually onto transfer paper P in the paper feed direction depending on the position of the paper cassette 16.
In the case of a certain copying machine wherein a three-stage paper cassette 16 is provided, for example, the length of the image transferred to transfer paper P of an A3 size of an intermediate stage in the paper feed direction becomes shorter by 0.3% in comparison with transfer paper P of the A3 size of the paper cassette of the upper stage. Similarly, the length of the image transferred to transfer paper of an A4R size of the paper cassette of the upper stage in the paper feed direction becomes longer by 0.1%.